Coated abrasives, which are a type of abrasive article, comprise a backing upon which a binder holds and supports a coating of abrasive grains. A typical coated abrasive comprises a "make" coat of a thermosetting resinous binder applied on the front surface of the backing in order to secure the abrasive grains to the backing, and a "size" coat of a thermosetting binder which can be applied over the make coat and abrasive grains in order to firmly bond the abrasive grains to the backing. The binder material of the size coat can be the same material as the binder material of the make coat or of a different material. Examples of typical make and size coats include phenolic resins, urea-formaldehyde resins, urethane resins, melamine-formaldehyde resins, epoxy resins and alkyd resins. The most widely used binder is a resole phenolic resin.
Examples of common coated abrasive backings include cloth, polymeric film, paper, vulcanized fiber, nonwoven webs and combinations and treated versions thereof. If the backing is cloth, the cloth is usually sealed, otherwise the make coat will penetrate into the cloth. The cloth is sealed or treated by applying one or more coats of an adhesive type material. Examples of typical treating adhesives include lattices, styrene-butadiene copolymers, glue, starches, phenolic resins, urea-formaldehyde resins, urethane resins, melamine-formaldehyde resins, epoxy resins and alkyd resins. Bonded abrasives which are a type of abrasive article, comprise abrasive grains bonded together by a binder to form a shaped mass. Nonwoven abrasives, which are a type of abrasive article comprise abrasive grains bonded to a nonwoven substrate.
In recent years, there has been an increasing demand for superabrasives both in the coated and bonded abrasive markets. Superabrasives are abrasive articles that employ abrasive grains that are superior in performance, i.e., greater than 20 times that of conventional abrasive grains in abrading difficult to grind materials such as tool steels or ceramics. Superabrasive grains are typically diamond or cubic boron nitride and these abrasive grains typically cost in excess of one thousand dollars per pound. Conventional abrasive grains include garnet, silicon carbide, silica, aluminum oxide, alumina zirconia, boron carbide, ceramic aluminum oxide and these conventional abrasive grains are typically less than ten dollars per pound. These superabrasive articles grind for periods of time much longer than those of conventional abrasive articles. Additionally, these superabrasive articles are usually used under wet abrading conditions. Thus the binder must have enough water resistance, strength, heat resistance and toughness in order to take full advantage of the superabrasive grain. If the binder fails prematurely, then full utilization of the superabrasive grains is not achieved.
U.S. Pat. No. 3,651,012 (Holub et al.) discusses a bismaleimide binder for use as insulation, protective applications and numerous molding applications. In column 13, line 33 to 45 it mentions that the bismaleimide binder can be used in bonded abrasives.
U.S. Pat. No. 3,615,303 (Singer et al.) discloses a coated abrasive backing treatment, referred to as an intermediate layer, which comprises an epoxide resin mixture based on a) 4,4' dihydroxydiphenyl-2,2-propane (Bisphenol A), b) an epoxide resin based on Bisphenol A internally plasticized by a reaction with castor oil, c) carbamic acid alkyl esters and d) a curing agent.
U.S. Pat. No. 4,047,903 (Hesse et al.) teaches a radiation curable binder comprising a resin prepared by at least partial reaction of (a) epoxy monomers having at least two epoxy groups e.g., from diphenylolpropane and epichlorohydrin, with (b) unsaturated monocarboxylic acids, and (c) optionally polycarboxylic acid anhydride.
U.S. Pat. No. 4,396,657 (Ibrahim) teaches an epoxy resin coatable from water with a dicyandiamide, blocked isocyanates, and/or imidazole curing agents for a saturant to impregnate the multifilament yarns of a stitchbonded coated abrasive backing.
U.S. Pat. No. 4,575,384 (Licht et al.) teaches that polyimide binders can be employed in a coated abrasive construction.
U.S. Pat. No. 4,588,419 (Caul) teaches an adhesive for coated abrasives comprising a mixture of: (a) electron beam radiation curable resin system comprising an oligomer selected from the group consisting of: urethane acrylates and epoxy acrylates, a filler and a diluent and (b) a thermally curable resin selected from the group consisting of: phenolic resins, melamine resins, amino resin, alkyd resins and furan resins.
U.S. Pat. No. 4,751,138 (Tumey et al.), assigned to the assignee of the present case, involves a coated abrasive in which either the make coat or the size coat comprises an ethylenically unsaturated compound, an epoxy monomer and a photoinitiator.
U.S. Pat. No. 4,684,678 (Schultz et al.), assigned to the assignee of the present case, teaches epoxy compositions that employ 9,9-bis(aminophenyl)fluorenes as curing agents. The resulting cured epoxy formulation has a high glass transition temperature, high ductility and low moisture pick-up.
U.S. Pat. No. 4,802,896 (Law et al.), assigned to the assignee of the present case, pertains to an abrasive bonding system comprising a thermosetting resin and a thermally stable, aromatic ligand. This aromatic ligand comprises a large aromatic moiety around a central metallic ion in a complex compound.
U.S. Pat. No. 4,822,464 (Pocius), assigned to the assignee of the present case, pertains to water compatible resins containing an aryl or cycloalkyl compound having a sufficiently bulky structure to raise the glass transition temperature of a cured epoxy resin by more than 20.degree. C.
U.S. Pat. No. 4,983,672 (Almer et al.), assigned to the assignee of the present case, teaches the use of a binder type material comprising 9,9-bis(hydroxyphenyl) fluorene and an epoxy resin.
However, the above references do not teach the use of a polycyclic aryl, polycyclic alkyl, cycloalkyl, and/or modified epoxy resin having high Tg, thermal resistance, and water resistance in an abrasive article.
A need thus exists in the abrasive industry for a water resistant, tough, heat resistant and strong thermosetting binder which is useful for abrasive articles, particularly superabrasive articles.